Projection aligner, aberration estimating mask pattern, aberration quantity estimating method, aberration eliminating filter and semiconductor manufacturing method

ABSTRACT

A projection aligner of the present invention, in which ultraviolet light emitted from a lamp housing is split by a fly-eye lens into a large number of point light sources which are independent of one another. Further, in this projection aligner, the light is shaped by an aperture, so that a secondary light source plane is formed. Moreover, after an exposure area is established by a blind, a photomask is illuminated. Thereafter, an image of a light source is formed on a pupillary surface of a projection optical system from light diffracted by the photomask. Furthermore, a wave front aberration is compensated by an aberration eliminating filter placed on the pupillary surface of the optical system of the projection aligner. Then, the image of a circuit pattern is formed on a wafer. Thereby, the influence of the aberration of the optical system is eliminated. Consequently, the high-accuracy transferring of the pattern can be achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection aligner for use in alarge-scale integrated circuit (LSI) manufacturing process. Moreover,the present invention relates to an aberration estimating (orevaluating) mask pattern for estimating aberration included in anoptical system of a projection aligner, an aberration quantity (namely,quantity-of-aberration) estimating method, and an aberration eliminatingfilter for eliminating the aberration. Furthermore, the presentinvention relates to a semiconductor manufacturing method formanufacturing a semiconductor device by transferring a circuit patternwhile eliminating the aberration.

2. Description of the Related Art

Projection aligners for projecting a circuit pattern of a semiconductordevice, which is formed on a mask, onto a wafer are required to havehigh resolution so as to achieve the transferring of a micro or finepattern thereon. Generally, in proportion as the numerical aperture (NA)of a projection lens (or projecting lens) increases, or in proportion asthe wavelength of exposure light decreases, the resolution is improved.The method of increasing the NA of the projection lens, however, causesa reduction in the focal depth (namely, the depth of focus) thereof atthe time of transferring the pattern. Thus, there is a limit to theimprovement of the resolution. On the other hand, the use of exposurelight having short wavelength requires an extensive modification of thetransferring process. The method of decreasing the wavelength ofexposure light is, therefore, unpractical.

Thus, in Japanese Patent Laid-Open Nos. 4-251914 and 4-179213, therehave been proposed projection aligners, by each of which the resolutioncan be enhanced by increasing the NA but, simultaneously, the focaldepth can be enlarged, by the applicant of the present application. Asillustrated in FIG. 19, in this projection aligner, a fly-eye lens 3 isplaced diagonally to the front of a lamp house or lamp housing 1 byinterposing a mirror 2 therebetween. Further, an aperture 4 ispositioned in front of the fly-eye lens 3. Moreover, a blind 6 is placedin front of the aperture 4 by putting a condensing lens or condenserlens 5 therebetween. Furthermore, a photomask 10, on which a desiredcircuit pattern is formed, is disposed diagonally to the front of theblind 6 by interposing a condensing lens 7, a mirror 8 and a condensinglens 9 therebetween. In addition, a wafer 12 is placed in front of thephotomask 10 by interposing a projection optical system or projectinglens system 11 therebetween. The contrast of an image at the time ofdefocusing is improved by putting a phase shift member, which isoperative to cause a phase difference between light passing through thecentral portion of a transmitting zone or area and light passing thoughthe peripheral area thereof, onto the pupillary surface or pupil planeof the projection optical system 11. Consequently, the focal depth isincreased effectively.

However, in the case of the aforementioned conventional projectionaligner, the aberration of the optical system is not taken intoconsideration. Generally, actual or practical optical systems havevarious aberrations. Typical aberrations are a spherical aberration, anastigmatism aberration, a field curvature and a coma aberration. It isknown that theses aberrations can be expressed, as illustrated in FIGS.20A to 20E, by being converted into wavefront aberrations, respectively.In these figures, φ denotes a shift quantity or distance of a wavefront;ρ a radius on a pupillary surface (namely, ηξE -plane); θ an angle ofrotation with respect to the axis η; y₀ coordinates on a wafer surface;and B to F constants. The details of these aberrations are described invarious literatures, for example, “Principle of Optics I to III”(published by Tokai University Press.).

Because the optical systems of the conventional projection aligners havesuch aberrations, the conventional projection aligners have the problemsthat the image quality thereof is degraded and that the accuracy oftransferring a circuit pattern is deteriorated.

The present invention is accomplished to solve such problems of theconventional projection aligners.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide aprojection aligner which can eliminate the influence of the aberrationsof the optical system thereof and can achieve the high-accuracy transferof a (circuit) pattern.

Moreover, another object of the present invention is to provide anaberration estimating mask pattern for estimating the aberration of theoptical system of a projection aligner, and to further provide a methodfor estimating an aberration quantity by using this aberrationestimating mask pattern.

Furthermore, still another object of the present invention is to providean aberration eliminating filter for compensating for an aberration ofthe optical system of the projection aligner.

Additionally, yet another object of the present invention is to providea semiconductor manufacturing method for manufacturing a semiconductordevice by transferring a circuit pattern while eliminating the influenceof the aberration of the optical system of a projection aligner.

To achieve the foregoing objects, in accordance with an aspect of thepresent invention, there is provided a projection aligner whichcomprises: a light source; an aperture for shaping illumination lightand forming a secondary light source plane; a blind having an openingportion for setting an exposure area; a photomask which has a circuitpattern and is illuminated with illumination light emanating from thesecondary light source plane; a projection optical system for projectinga circuit pattern of the photomask by forming an image on an exposedsubstrate from diffraction light diffracted by the photomask; and anaberration eliminating filter, placed on a pupillary surface of theprojection optical system, for eliminating an aberration.

Further, in accordance with another aspect of the present invention,there is provided an aberration estimating mask pattern which comprises:a transparent substrate; a plurality of micro patterns selectivelyformed on the transparent substrate; and a plurality of larger patternswhich are formed selectively on the transparent substrate. Further, inthis aberration estimating mask pattern, each of the micro patterns anda corresponding one of the larger patterns are combined with each other.Furthermore, a plurality of such combinations (or sets) of micropatterns and a larger pattern are placed on the transparent substrate.

Moreover, in accordance with a further aspect of the present invention,there is provided an aberration quantity (namely, aquantity-of-aberration) estimating method which comprises the steps of:exposing aberration estimating mask patterns; observing a plurality offinished (or obtained) patterns; finding a best focus position or afinishing position of each of the patterns; and estimating a quantity ofan aberration from a quantity of a change in the best focus position orin the finishing position of each of the patterns.

Furthermore, in accordance with yet another aspect of the presentinvention, there is provided an aberration eliminating filter that is afilter, which is placed on a pupillary surface (namely, a pupil plane)of a projection optical system, for eliminating an aberration. Thisfilter is provided with a transparent substrate and a wavefrontregulating (or adjusting) transparent multi-layer film formed on atleast one principal plane.

Additionally, in accordance with a further aspect of the presentinvention, there is provided a semiconductor manufacturing method whichcomprises the steps of: forming a secondary light source plane byshaping illumination light emanating from a light source; establishingan exposure area; illuminating a photomask with illumination lightemanating from a secondary light source plane; forming an image of alight source on a pupillary surface from light diffracted by the mask;compensating a wavefront aberration on the pupillary surface of aprojection optical system; and manufacturing a semiconductor device byprojecting a circuit pattern onto a wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects and advantages of the present invention willbecome apparent from the following description of preferred embodimentswith reference to the drawings in which like reference charactersdesignate like or corresponding parts throughout several views, and inwhich:

FIG. 1 is a diagram for illustrating the configuration of a projectionaligner embodying the present invention, namely, Embodiment 1 of thepresent invention;

FIG. 2 is a flowchart for illustrating a projection exposure methodembodying the present invention, namely, Embodiment 2 of the presentinvention;

FIG. 3A is a plan view of an aberration estimating mask patternembodying the present invention, namely, Embodiment 3 of the presentinvention;

FIG. 3B is a diagram for illustrating a transferred pattern which isobtained when exposing the mask pattern of FIG. 3A;

FIGS. 4A and 4B are diagrams for illustrating the best focus positionsof a micro pattern and that of a larger pattern, respectively, which areobtained according to a spherical aberration estimating method embodyingthe present invention, namely, Embodiment 4 of the present invention;

FIGS. 5A and 5B are diagrams for illustrating the best focus positionsof a lateral pattern element (namely, a lateral pattern side) and thatof a longitudinal pattern element (namely, a longitudinal pattern side),respectively, which are obtained according to an astigmatism estimatingmethod embodying the present invention, namely, Embodiment 5 of thepresent invention;

FIGS. 6A and 6B are diagrams for illustrating the best focus positionsof a micro pattern and that of a larger pattern, respectively, which areobtained according to a field curvature estimating method embodying thepresent invention, namely, Embodiment 6 of the present invention;

FIG. 7 is a diagram which shows a transferring pattern for illustratinga coma (aberration) estimating method embodying the present invention,namely, Embodiment 7 of the present invention;

FIG. 8 is a diagram which shows a transferring pattern for illustratinga distortion aberration estimating method embodying the presentinvention, namely, Embodiment 8 of the present invention;

FIGS. 9A and 9B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 10 of the present invention for compensating a positivespherical aberration;

FIGS. 10A and 10B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 11 of the present invention for compensating a negativespherical aberration;

FIGS. 11A and 11B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 12 of the present invention for compensating a positiveastigmatism aberration;

FIGS. 12A and 12B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 13 of the present invention for compensating a negativeastigmatism aberration;

FIGS. 13A and 13B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 14 of the present invention for compensating a positive fieldcurvature;

FIGS. 14A and 14B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 15 of the present invention for compensating a negative fieldcurvature;

FIGS. 15A and 15B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 16 of the present invention for compensating a distortionaberration;

FIGS. 16A and 16B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 17 of the present invention for compensating a comaaberration;

FIGS. 17A and 17B are a sectional view and a perspective view of anaberration eliminating filter embodying the present invention, namely,Embodiment 18 of the present invention;

FIG. 18 is a perspective diagram for illustrating a shift in wavefrontin the case that various kinds of aberrations are synthesizes inEmbodiment 19 of the present invention;

FIG. 19 is a diagram for illustrating the configuration of theconventional projection aligner; and

FIGS. 20A to 20E are diagrams for illustrating a spherical aberration,an astigmatism aberration, a field curvature, a distortion aberrationand a coma aberration on a pupil, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail by referring to the accompanying drawings.

Embodiment 1

FIG. 1 is a diagram for illustrating the configuration of a projectionaligner embodying the present invention, namely, Embodiment 1 of thepresent invention. As illustrated in this figure, in this projectionaligner, a fly-eye lens 3 is placed diagonally to the front of a lamphousing or house 1 by putting a mirror 2 therebetween. Further, anaperture 4 is positioned in front of the fly-eye lens 3. Moreover, ablind 6 is disposed in front of the aperture 4 by placing a condensinglens 5 therebetween. Furthermore, a photomask 10, on which a desiredcircuit pattern is formed, is placed diagonally to the front of theblind 6 by interposing the condensing lens 7, a mirror 8 and acondensing lens 9 therebetween. In addition, a wafer 12, from which anexposed substrate is obtained, is placed diagonally to the front of thephotomask 10 by putting a projection optical system 11 therebetween.Further, an aberration eliminating filter 1 for compensating foraberrations of the projection optical system 11 is put on the pupillarysurface or pupil plane of the projection optical system. Incidentally, alight source emanating ultraviolet light, such as a mercury vapor lampor an excimer laser, is used in the lamp housing 1.

Next, a semiconductor manufacturing method using this projection alignerwill be described hereinbelow. Ultraviolet light emitted from the lamphousing 1 reaches the fly-eye lens 3 through the mirror 2. Hereupon, theultraviolet light is split into a large number of point light sources(namely, light beams) which are independent of one another. Then, thelight rays emanating from these point light sources are shaped by theaperture 4, so that a secondary light source plane is formed.Thereafter, an exposure area is established by the blind 6. Moreover,the photomask 10 is illuminated through the condensing lenses 5, 7 and8. Thus, an image of the light source is formed on the pupillary surfaceof the projection optical system 11 from the light diffracted by thephotomask 10. Here, the aberration eliminating filter 13 is placed onthe pupillary surface of the projection optical system 11. Consequently,the wavefront aberration is compensated for on the pupillary surface.Thus, an image of a circuit pattern is formed on the wafer 12 from thediffracted light, the aberration of which is compensated for. At thattime, the aberration is compensated for on the pupillary surface of theprojection optical system by the aberration eliminating filter 13.Consequently, ill effects due to the aberrations can be removed.Thereby, good image characteristics can be obtained.

In this way, a circuit pattern is transferred onto the surface of thewafer 12. Further, after undergoing various processes such as a thinfilm deposition process, an etching process and an impurity diffusionprocess, a semiconductor device is produced.

Embodiment 2

A projection exposure method embodying the present invention, namely,Embodiment 2 of the present invention is illustrated by the flowchart ofFIG. 2. First, in step S1, an aberration estimating pattern is exposedto light so as to estimate or evaluate aberrations of an optical system.Next, in step S2, a post-exposure pattern or development patternobtained by the exposure is observed through a SEM (Scanning ElectronMicroscope). As a result of this observation, it is determined whatkinds or classifications of aberrations are combined with one another(namely, are contained or included) and occur in the optical system.Further, it is determined in step S4 what kind of the aberration isdominant between or among the aberrations of the projection opticalsystem. In subsequent step S5, an aberration eliminating filter forcompensating for the dominant aberration is selected. Then, theaberration eliminating filter selected in this way is inserted in(namely, is put onto) the pupillary surface of the projection opticalsystem in step S6. Subsequently, a circuit pattern is exposed to lightin step S7.

Thus, the aberration, which is dominant in the projection opticalsystem, can be selectively eliminated and good image characteristics canbe obtained by employing such an exposure method.

Embodiment 3

The aberration estimating mask used in the exposure method of Embodiment2 is illustrated in FIG. 3A. As shown in this figure, twenty-fiverectangular larger patterns 22 in total, which are placed in fivecolumns and five rows, are formed on a transparent substrate 21.Further, in each of the larger patterns 22, nine micro patterns 23 intotal, which are placed in three columns and three rows, are formed.Each of the larger patterns 22 has a dimension which is three times theexposure wavelength or so. Namely, twenty-five combinations of each ofthe larger patterns 22 and the micro patterns 23 arranged therein areplaced on the transparent substrate 21.

When this aberration eliminating mask pattern is exposed to light bymeans of an aplanatic lens, the corners of each of the larger patternsare rounded off owing to the diffraction. Thus, a transferring pattern,which contains larger patterns 32 and micro patterns 33 as shown in FIG.3B, is obtained. Generally, micro patterns are sensitive to aberrations,whereas large patterns are insensitive to aberrations. Thus, lensaberrations can be classified into five kinds easily and clearly byobserving the larger patterns 32 and the micro patterns 33 contained inthe transferring pattern.

Embodiment 4

A method for estimating a spherical aberration by using the aberrationestimating mask pattern of FIG. 3A will be described hereinbelow. First,the aberration estimating mask pattern is exposed to light by changingthe focusing conditions thereof. Then, finished twenty-five transferringpatterns are observed by means of a SEM or the like. Thereby, asillustrated in FIG. 4A, the best focus positions of the micro patterns33 are obtained at twenty-five points. Moreover, as illustrated in FIG.4B, the best focus positions of the larger patterns 32 are obtained attwenty-five points.

At that time, if it is observed that the best focus position is shiftedamong the micro patterns 33 and the larger patterns 32, a sphericalaberration of an exposure optical system proves to be present therein.Moreover, the quantity of the spherical aberration can be estimated fromthe quantity of the shift of the best focus position among the micropatterns 33 and the larger patterns 32.

Embodiment 5

A method for estimating an astigmatism aberration by using theaberration estimating mask pattern of FIG. 3A will be describedhereunder. First, the aberration estimating mask pattern is exposed tolight by changing the focusing conditions. Then, twenty-five finishedtransferring patterns are observed by means of a SEM or the like.Thereby, the best focus position of a lateral pattern element (or side)of each pattern is obtained at each of twenty-five points, asillustrated in FIG. 5A. Moreover, the best focus position of alongitudinal pattern element (or side) of each pattern is obtained ateach of the twenty-five points, as illustrated in FIG. 5B.

At that time, if it is observed that the best focus position is shiftedbetween the lateral pattern element and the longitudinal patternelement, an astigmatism aberration of an exposure optical system provesto be present therein. Moreover, the quantity of the astigmatismaberration can be estimated from a quantity of a shift (or variation) ofthe best focus position between the lateral pattern element and thelongitudinal pattern element.

Embodiment 6

A method for estimating a field curvature by using the aberrationestimating mask pattern of FIG. 3A will be described hereinbelow. First,the aberration estimating mask pattern is exposed to light by changingthe focusing conditions thereof. Then, finished twenty-five transferringpatterns are observed by means of a SEM or the like. Thereby, asillustrated in FIG. 6A, the best focus positions of the micro patterns23 are obtained at twenty-five points, respectively. Moreover, asillustrated in FIG. 6B, the best focus positions of the larger patterns22 are obtained at twenty-five points, respectively.

At that time, if it is observed that the best focus position of themicro pattern 33 coincides with that of the corresponding larger pattern32 at each of the twenty-five points but the best focus positions varydepending on the exposed position, for example, vary among the largerpatterns 32 placed at the twenty-five points, a field curvature of anexposure optical system proves to be present. Incidentally, the quantityof the field curvature can be estimated from the quantity of thevariation in the best focus position among the larger patterns 32.

Embodiment 7

A method for estimating a coma aberration by using the aberrationestimating mask pattern of FIG. 3A will be described hereinbelow. Theaberration estimating mask pattern is fist exposed to light by changingthe focusing conditions thereof. Then, twenty-five transferring patternsfinished as shown in FIG. 7 are observed by means of a SEM or the like.Thereby, the finished positions of the micro patterns 33 are obtained attwenty-five points, respectively.

At that time, if it is observed that the finished positions of the micropatterns 33 vary with respect to the finished position of thecorresponding larger pattern 32 as illustrated in FIG. 7, a comaaberration of an exposure optical system proves to be present therein.Moreover, the quantity of the coma aberration can be estimated from thequantity or distance of a relative shift between the finished positionof one of the larger patterns 32 and that of one of the correspondingmicro patterns 33 combined with the one of the larger patterns 32.

Embodiment 8

A method for estimating a distortion aberration by using the aberrationestimating mask pattern of FIG. 3A will be described hereinbelow. Theaberration estimating mask pattern is first exposed to light by changingthe focusing conditions thereof. Then, twentyfive transferring patternsfinished as shown in FIG. 8 are observed by means of a SEM or the like.Consequently, the finished positions of the micro patterns 33 areobtained at twenty-five points, respectively.

At that time, if it is observed that although the relative finishedposition of each of the larger pattern 32 with respect to the finishedposition of each of the corresponding micro patterns 33 is maintained(or unchanged), the finished positions of, for example, the largerpatterns 32 vary depending on the exposed positions thereof among thepatterns 32 respectively corresponding to the twenty-five points, asillustrated in FIG. 8, a distortion aberration of an exposure opticalsystem proves to be present therein. Moreover, the quantity of thedistortion aberration can be estimated from the quantities or distancesof shifts of the finished positions of the larger patterns 32.

Embodiment 9

A transparent substrate, on at least one principal plane of which atransparent multi-layer film for regulating a wavefront is formed, canbe used as the aberration eliminating filter 13 used in the projectionaligner of Embodiment 1, the aforesaid semiconductor manufacturingmethod of the present invention, or the projection exposure method ofEmbodiment 2. The transparent multi-film has a film thicknessdistribution, by which the wavefront shift occurring due to theaberration of a projection optical system can be compensated for.

Embodiment 10

An aberration eliminating filter for compensating for positive sphericalaberrations is illustrated in FIGS. 9A and 9B, as a practical example ofthe aberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 51 is formed on the surface of atransparent substrate 41. As illustrated in FIG. 20A, if a sphericalaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is represented orgiven by an equation φ=−Bρ⁴/4. Thus, the transparent multi-layer film 51for compensating for positive spherical aberrations is shaped like amortar (namely, is cone-shaped) and has concentric-ring-like layers asillustrated in FIG. 9B, and further has a longitudinal section, whoseshape is like that of a section of the mortar and is represented by apositive quartic function as shown in FIG. 9A. A positive sphericalaberration can be eliminated by putting this aberration eliminatingfilter onto the pupillary surface of the projection optical system.Consequently, the image quality can be improved.

Embodiment 11

An aberration eliminating filter for compensating for negative sphericalaberrations is illustrated in FIGS. 10A and 10B, as a practical exampleof the aberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 52 is formed on the surface of atransparent substrate 42. As illustrated in FIG. 20A, if a sphericalaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed orobtained by an equation φ=−Bρ⁴/4. Thus, the transparent multi-layer film52 for compensating for negative spherical aberrations is shaped like adome and has concentric-circle-like layers as illustrated in FIG. 10B,and further has a longitudinal section, whose shape is like that of asection of the dome and is represented by a negative quartic function asshown in FIG. 10A. A negative spherical aberration can be eliminated byputting this aberration eliminating filter onto the pupillary surface ofthe projection optical system. Consequently, the image quality can beenhanced.

Embodiment 12

An aberration eliminating filter for compensating for positiveastigmatism aberrations is illustrated in FIGS. 11A and 11B, as apractical example of the aberration eliminating filter of Embodiment 9.As shown in these figures, in the case of this aberration eliminatingfilter, a transparent multi-layer film 53 is formed on the surface of atransparent substrate 43. As illustrated in FIG. 20B, if an astigmatismaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed by anequation φ=−Cy₀ρ²cos²θ. Thus, the transparent multi-layer film 53 forcompensating for positive astigmatism aberrations has a shape concavedlike a mortar only in one direction, namely, is shaped like a saddle asillustrated in FIG. 20B, and further has a longitudinal section, whoseshape is like that of a section of a mortar only in a direction and isrepresented by a positive quadratic function as shown in FIG. 11A. Apositive astigmatism aberration can be eliminated by putting thisaberration eliminating filter onto the pupillary surface of theprojection optical system. Consequently, the image quality can beimproved.

Embodiment 13

An aberration eliminating filter for compensating for negativeastigmatism aberrations is illustrated in FIGS. 12A and 12B, as apractical example of the aberration eliminating filter of Embodiment 9.As shown in these figures, in the case of this aberration eliminatingfilter, a transparent multi-layer film 54 is formed on the surface of atransparent substrate 44. As illustrated in FIG. 20B, if an astigmatismaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed by anequation φ=−Cy₀ρ²cos²θ. Thus, the transparent multi-layer film 53 forcompensating for positive astigmatism aberrations has a shape which isconvex like a dome only in one direction as illustrated in FIG. 20B, andfurther has a longitudinal section, whose shape is like that of asection of the dome only in a direction and is represented by a negativequadratic function as shown in FIG. 11A. A negative astigmatismaberration can be eliminated by putting this aberration eliminatingfilter onto the pupillary surface of the projection optical system.Consequently, the image quality can be improved.

Embodiment 14

An aberration eliminating filter for compensating for positive fieldcurvatures is illustrated in FIGS. 13A and 13B, as a practical exampleof the aberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 55 is formed on the surface of atransparent substrate 45. As illustrated in FIG. 20C, if a fieldcurvature aberration is converted into a wavefront aberration on apupillary surface, the quantity φ of a shift of the wavefront isexpressed by an equation φ=−Dy₀ ²ρ²/2. Thus, the transparent multi-layerfilm 55 for compensating for positive field curvatures is shaped like amortar and has concentric-ring-like layers as illustrated in FIG. 13B,and further has a longitudinal section, whose shape is like that of asection of the mortar and is represented by a positive quadraticfunction as shown in FIG. 13A. A positive field curvature can beeliminated by putting this aberration eliminating filter onto thepupillary surface of the projection optical system. Consequently, theimage quality can be improved.

Embodiment 15

An aberration eliminating filter for compensating for negative fieldcurvatures is illustrated in FIGS. 14A and 14B, as a practical exampleof the aberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 56 is formed on the surface of atransparent substrate 46. As illustrated in FIG. 20C, if a fieldcurvature is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed by anequation: φ=−Dy₀ ²ρ²/2. Thus, the transparent multi-layer film 55 forcompensating for negative field curvatures is shaped like a dome and hasconcentric-circle-like layers as illustrated in FIG. 14B, and furtherhas a longitudinal section, whose shape is like that of a section of thedome and is represented by a negative quadratic function as shown inFIG. 14A. A negative field curvature can be eliminated by putting thisaberration eliminating filter onto the pupillary surface of theprojection optical system. Consequently, the image quality can beimproved.

Embodiment 16

An aberration eliminating filter for compensating for distortionaberrations is illustrated in FIGS. 15A and 15B, as a practical exampleof the aberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 57 is formed on the surface of atransparent substrate 47. As illustrated in FIG. 20D, if a distortionaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed by anequation φ=Ey₀ ³ρ cos θ. Thus, the transparent multi-layer film 57 forcompensating for distortion aberrations has a shape like a planeinclined only in one direction as illustrated in FIG. 15B, and furtherhas a longitudinal section, whose shape is like that of a section of theinclined plane represented by a linear function as shown in FIG. 15A. Adistortion aberration can be eliminated by putting this aberrationeliminating filter onto the pupillary surface of the projection opticalsystem. Consequently, the image quality can be improved.

Embodiment 17

An aberration eliminating filter for compensating for coma aberrationsis illustrated in FIGS. 16A and 16B, as a practical example of theaberration eliminating filter of Embodiment 9. As shown in thesefigures, in the case of this aberration eliminating filter, atransparent multi-layer film 58 is formed on the surface of atransparent substrate 48. As illustrated in FIG. 20E, if a distortionaberration is converted into a wavefront aberration on a pupillarysurface, the quantity φ of a shift of the wavefront is expressed by anequation φ=Fy₀ρ³. Thus, the transparent multi-layer film 57 forcompensating for coma aberrations is shaped like a slope inclined onlyin one direction as illustrated in FIG. 16B, and further has alongitudinal section, whose shape is that of the slope represented by acubic function as shown in FIG. 16A. A coma aberration can be eliminatedby putting this aberration eliminating filter onto the pupillary surfaceof the projection optical system. Consequently, the image quality can beimproved.

Embodiment 18

In the case that a plurality of kinds of aberrations coexist, anappropriate combination of some of the aberration eliminating filtersdescribed hereinabove as Embodiment 10 to Embodiment 17 may be used. Forexample, as illustrated in FIGS. 17A and 17B, if the aberrationeliminating filter used in Embodiment 15 for compensating for a negativefield curvature is combined with the aberration eliminating filter usedin Embodiment 17 for compensating for a coma aberration, a negativefield curvature and a coma aberration can be simultaneously compensatedfor. Generally, in an actual optical system, various kinds ofaberrations coexist. Thus, all of the various kinds of aberrations canbe eliminated by suitably combining the aberration eliminating filtersdescribed hereinbefore as Embodiment 10 to Embodiment 17 with oneanother. Consequently, the image quality can be improved.

Embodiment 19

In accordance with the present invention, there can be produced acomposite aberration eliminating filter having characteristicscompensating for a shift of the wavefront which is obtained bysynthesizing the quantities of aberrations, namely, the shifts of thewavefronts estimated by the method of one of Embodiment 4 to Embodiment8 as illustrated in FIG. 18. For instance, such an aberrationeliminating filter can be produced by forming a transparent multi-layerfilm, which has a sectional shape corresponding to the synthesized shiftof the wavefront as illustrated in FIG. 18, on a transparent substrate.

All of the various kinds of aberrations are eliminated by introducingthis composite aberration eliminating filter into the projectionaligned. The image quality can be enhanced.

What is claimed is:
 1. A spherical aberration quantity estimatingmethod, comprising the steps of: exposing an aberration estimating maskpattern using photoresist and an optical projection system, theaberration estimating mask pattern including: a transparent substrate; aplurality of micro patterns selectively formed on the transparentsubstrate, each micro pattern having a dimension which is on the orderof an exposure wavelength; and a plurality of larger patterns which areselectively formed on the transparent substrate, each larger patternhaving a size which is more than three times the exposure wavelength;wherein each of the micro patterns and a corresponding one of the largerpatterns are combined with each other, wherein a plurality ofcombinations of the micro patterns and the larger pattern are placed onthe transparent substrate; observing a plurality of finished micropatterns and larger patterns through a Scanning Electron Microscope;finding a best focus position of each of the micro patterns; finding abest focus position of each of the larger patterns; measuring a quantityof a shift of the best focus position among the micro patterns and amongthe larger patterns; and estimating a quantity of the sphericalaberration from the quantity of the shift of the best focus position forboth the micro and larger patterns as a function of positioning in theestimating mask pattern.
 2. An astigmatism aberration quantityestimating method, comprising the steps of: exposing an aberrationestimating mask pattern using photoresist and an optical projectionsystem, the aberration estimating mask pattern including: a transparentsubstrate; a plurality of micro patterns selectively formed on thetransparent substrate, each micro pattern having a dimension which is onthe order of an exposure wavelength; and a plurality of larger patternswhich are selectively formed on the transparent substrate, each largerpattern having a size which is more than three times the exposurewavelength; wherein each of the micro patterns and a corresponding oneof the larger patterns are combined with each other, wherein a pluralityof combinations of the micro patterns and the larger pattern are placedon the transparent substrate; observing the exposed plurality offinished micro patterns and larger patterns through a Scanning ElectronMicroscope; finding a best focus position of a longitudinal patternelement of each of the micro and larger patterns; finding a best focusposition of a lateral pattern element of each of the micro and largerpatterns; measuring a quantity of a shift of the best focus positionbetween the longitudinal pattern element and the lateral pattern elementof each of the micro and larger patterns; and estimating a quantity ofthe astigmatism aberration from the quantity of the shift of the bestfocus position for both the micro and larger patterns as a function ofpositioning in the estimating mask pattern.
 3. A field curvaturequantity estimating method, comprising the steps of: exposing anaberration estimating mask pattern using photoresist and an opticalprojection system, the aberration estimating mask pattern including: atransparent substrate; a plurality of micro patterns selectively formedon the transparent substrate, each micro pattern having a dimensionwhich is on the order of an exposure wavelength; and a plurality oflarger patterns which are selectively formed on the transparentsubstrate, each larger pattern having a size which is more than threetimes the exposure wavelength; wherein each of the micro patterns and acorresponding one of the larger patterns are combined with each other,wherein a plurality of combinations of the micro patterns and the largerpattern are placed on the transparent substrate; observing the exposedplurality of finished micro patterns and larger patterns through aScanning Electron Microscope; finding a best focus position of each ofthe larger patterns; and estimating a quantity of the field curvaturefrom a quantity of a variation in the best focus position among only theplurality of larger patterns as a function of position in the estimatingmask pattern.
 4. A coma aberration quantity estimating method,comprising the steps of: exposing an aberration estimating mask patternusing photoresist and an optical projection system, the aberrationestimating mask pattern including; a transparent substrate: a pluralityof micro patterns selectively formed on the transparent substrate, eachmicro pattern having a dimension which is on the order of an exposurewavelength; and a plurality of larger patterns which are selectivelyformed on the transparent substrate, each larger pattern having a sizewhich is more than three times the exposure wavelength; wherein each ofthe micro patterns and a corresponding one of the larger patterns arecombined with each other, wherein a plurality of combinations of themicro patterns and the larger pattern are placed on the transparentsubstrate; observing the exposed plurality of finished micro patternsand larger patterns through a Scanning Electron Microscope; finding afinishing position of each of the micro patterns; finding a finishingposition of each of the larger patterns; and estimating a quantity ofthe coma aberration from a relative variation in the finishing positionbetween the micro pattern and the corresponding larger pattern as afunction of position in the estimatingmask pattern.
 5. A distortionaberration quantity estimating method, comprising the steps of: exposingan aberration estimating mask pattern using photoresist and an opticalprojection system, the aberration estimating mask pattern including: atransparent substrate; a plurality of micro patterns selectively formedon the transparent substrate, each micro pattern having a dimensionwhich is on the order of an exposure wavelength; and a plurality oflarger patterns which are selectively formed on the transparentsubstrate, each larger pattern having a size which is more than threetimes the exposure wavelength; wherein each of the micro patterns and acorresponding one of the larger patterns are combined with each other,wherein a plurality of combinations of the micro patterns and the largerpattern are placed on the transparent substrate; observing the exposedplurality of finished micro patterns and larger patterns through aScanning Electron Microscope; finding a finishing position of each ofthe larger patterns; and estimating a quantity of the distortionaberration from a quantity of a variation in the finishing positionbetween only the plurality of larger patterns as a function of positionin the estimating mask pattern.